Open Rocket Effect of Tail Cone on Stability

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WoShuGui

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In my Broken Arrow XP simulation the extended Barrowman method in Open Rocket moves the CP forward quite a bit when a tail cone is added. Is this realistic?

With the tail cone, stability is 0.159 cal:
View attachment 253234

Remove the tail cone leaving everything else unchanged, stability is 0.933 cal:
View attachment 253235

This difference is all due to the CP moving forward. That comes out to 19 additional ounces of nose weight (16 ounces already) just because there is a tail cone, so I am a little skeptical of what the simulation is saying.
 
Yep..... tailcone will do that.
I had my fins mounted 3in from rear of tube & my stability tanked.
I removed all but a 1/2in from rear to get it back on track.
I wanted to keep it due to adding 1000 ft per 10,000 and I was going for altitude.

Is this a motor retention tailcone [Aero-Pac] ? I have not had much problem with those. Or something else.
I used tailcone closures on motors for minimum diameter project where the problem was really pronounced.

Your stability seems off for that kit.
I would double check my weights and materials shown in the sim program against actually weighing the parts.
 
Is this a motor retention tailcone [Aero-Pac] ? I have not had much problem with those. Or something else.
I used tailcone closures on motors for minimum diameter project where the problem was really pronounced.

Your stability seems off for that kit.
I would double check my weights and materials shown in the sim program against actually weighing the parts.

Yes, this is an Aero-Pac tail cone. So... I finally got around to measuring and weighing everything to get a more exact simulation; but pretty much the same result. Per Open Rocket, it needs ~20 extra ounces of nose weight with the tail cone, so any altitude benefit is basically lost. Seems a waste of a nice tail cone, but I have already assembled the motor mount so there is no going back. Kind of has killed my enthusiasm for the project for the moment.

Edit: I went back and measured the actual taper on the Aero-Pac tail cone. Turns out I had it tapering down to 3" (the motor diameter) in the sim, but it actually tapers down to 3.625" which is much more gentle. Now the sim only requires ~8 extra ounces of nose weight with the tail cone.
 
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I've seen that rocket with tail-cone fly, but don't know if any weight was added.

I would call RW and ask about your situation before going any further. Maybe someone there can shed some light on it for you.
 
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